One of my players is trying to use the Artificer's infusion with a blunderbuss, but it won't allow them to because the weapon lacks the Ammunition property. Given the blunderbuss is described as using ammunition and even a separate ammunition item exists for it, I think this is a bug. 

Quote from Gulaghar >>

One of my players is trying to use the Artificer's infusion with a blunderbuss, but it won't allow them to because the weapon lacks the Ammunition property. Given the blunderbuss is described as using ammunition and even a separate ammunition item exists for it, I think this is a bug. 

 It is not a bug. The weapon does not actually have the ammunition property as it follows different rules. None of the firearms from Wildmount have the Ammunition property.

That doesn't make much sense. They're weapons that use ammunition and are described as such. But if that's how it's printed in the book, I suppose that's how it is, even if I'd call it an obvious mistake. 

Quote from Gulaghar >>

That doesn't make much sense. They're weapons that use ammunition and are described as such. But if that's how it's printed in the book, I suppose that's how it is, even if I'd call it an obvious mistake. 

 It wasn’t a mistake, it was intentional. Using ammunition is not the same as the ammunition rule.

Ammunition. You can use a weapon that has the ammunition property to make a ranged attack only if you have ammunition to fire from the weapon. Each time you attack with the weapon, you expend one piece of ammunition. Drawing the ammunition from a quiver, case, or other container is part of the attack (you need a free hand to load a one-handed weapon). At the end of the battle, you can recover half your expended ammunition by taking a minute to search the battlefield.

If you use a weapon that has the ammunition property to make a melee attack, you treat the weapon as an improvised weapon (see "Improvised Weapons" later in the section). A sling must be loaded to deal any damage when used in this way.

The blunderbuss uses different rules.

Reload. The weapon can be fired a number of times equal to its Reload score before you must spend 1 attack or 1 action to reload. You must have one free hand to reload a firearm.

Misfire. Whenever you make an attack roll with a firearm, and the dice roll is equal to or lower than the weapon’s Misfire score, the weapon misfires. The attack misses, and the weapon cannot be used again until you spend an action to try and repair it. To repair your firearm, you must make a successful Tinker’s Tools check (DC equal to 8 + misfire score). If your check fails, the weapon is broken and must be mended out of combat at a quarter of the cost of the firearm. Creatures who use a firearm without being proficient increase the weapon’s misfire score by 1.

Explosive. Upon a hit, everything within 5 ft of the target must make a Dexterity saving throw (DC equal to 8 + your proficiency bonus + your Dexterity modifier) or suffer 1d8 fire damage. If the weapon misses, the ammunition fails to detonate, or bounces away harmlessly before doing so.

Ammunition
All firearms require ammunition to make an attack, and due to their rare nature, ammunition may be near impossible to find or purchase. However, if materials are gathered, you can craft ammunition yourself using your Tinker’s Tools at half the cost. Each firearm uses its own unique ammunition and is generally sold or crafted in batches listed below next to the price.

The Blunderbuss is a non-official firearm from the gunslinger class. Those firearms use different rules from those found in the Dungeon Master's Guide, one of those differences being they don't use the ammunition property. This renders them incompatible with certain things like the artificers Repeating Shot infusion. This is how Matt Mercer designed the weapons.